It is thoughtful to choose a pearl necklace for my mother, but whether it is suitable as a gift depends on my mother's personal preference and family culture. If your mother likes pearl jewelry or appreciates expensive gifts, it may be a good choice to send a pearl necklace.

However, if you are not sure whether your mother likes or accepts pearl jewelry, or if your family doesn't value expensive gifts, it may be more appropriate to choose a more moderate gift. According to mom's hobbies or other related factors, you can choose some gifts that are more practical or in line with her taste.

Most importantly, when choosing a gift, you should consider and respect the preferences and values of the recipient. Try to discuss with your girlfriend and learn more about your mother's preferences in order to make the most appropriate decision.